3123 - Improving Resectability and Prognosis in Initially Unresectable Locally Advanced Colon Cancer through Neoadjuvant Chemoradiotherapy: A Single-Center Retrospective Study

Z. T. Zhang¹, X. Tian¹, Y. Liu¹, Q. X. Wang¹, H. Chang¹, W. Xiao¹, R. X. Zhang², R. L. Li², J. X. Wu², Z. Lu², R. Zhang³, and Y. Gao¹; ¹Department of Radiation Oncology, Sun Yat-sen University Cancer Center, Guangzhou, China, ²Department of Colorectal Surgery, Sun Yat-sen University Cancer Center, Guangzhou, China, ³Department of Endoscopy, Sun Yat-sen University Cancer Center, Guangzhou, China

Purpose/Objective(s): Patients with locally advanced colon cancer (LACC) have a poor prognosis and face challenges in complete resection of the tumor. Currently, options for downstaging treatment for patients with unresectable LACC are limited, yet the conversion rate to resectable status is crucial for patient survival. This study aims to evaluate the feasibility and efficacy of neoadjuvant chemoradiotherapy (NACRT) in patients with initially unresectable LACC. It is the largest single-center retrospective study to date. Materials/

Methods: We included 181 patients diagnosed with initially unresectable LACC at a single institution between 2010 and 2023, who received NACRT. Unresectability was determined by multidisciplinary team discussion according to image examination or confirmed by exploratory laparotomy. Most patients received a daily irradiation (GTV 45-50 Gy/25F/5W) with XELOX regimen chemotherapy every 3 weeks for 4 cycles. Surgery scheduled 6–8 weeks after radiotherapy and adjuvant chemotherapy were given if patients converted to resectable LACC. Surgical conversion rates, R0 resection rates, and pathological complete response (pCR) rates were calculated to evaluate short-term efficacy. Overall survival (OS), progression-free survival (PFS), local control (LC), and disease-free survival (DFS) were calculated to evaluate long-term efficacy. Acute toxicities during NACRT and postoperative complications were assessed to evaluate treatment safety.
Results: Of the patients, 155 (85.6%) underwent surgical resection of the primary tumor after receiving NACRT, with 147 (81.2%) achieving R0 resection and 29 (16.0%) achieving pCR. Twenty-six patients (14.4%) underwent exploratory laparotomy or abandoned surgery. 81.5% (57/70) of patients initially diagnosed with bladder invasion avoided radical cystectomy. The median follow-up time was 71.6 months. The 5-year OS, 5-year PFS, and 5-year LC for the whole group were 74.4%, 64.4%, and 87.9%, respectively. The 5-year DFS after R0 resection was 73.8%. The 5-year OS for patients with R0 resection was significantly higher than for those who did not achieve R0 resection (83.8% vs 31.1%, p<.001), while there were no significant survival differences between patients with left-sided versus right-sided colon cancer or between pMMR/dMMR status. During NACRT, the incidences of grade 3-4 myelosuppression, mucositis/dermatitis, and gastrointestinal toxicity were 19.3%, 2.2%, and 6.1%, respectively. Three patients experienced anastomotic leakage after surgery.
Conclusion: NACRT followed by radical surgery is safe and feasible for patients with initially unresectable LACC. NACRT as a conversion therapy achieves a high rate of tumor downstaging, R0 resection and long-term survival with acceptable toxicity.